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MS2 Renal > 9/8- Review of Renal Physiology > Flashcards

9/8- Review of Renal Physiology Flashcards

1
Q

T/F: there are a few, scattered glomeruli in the renal medulla?

A

False; the renal medulla = tubules + vessels (no glomeruli)

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2
Q

Describe the vasculature of the kidney?

A

Renal artery -> afferent arteriole -> glomerula caps -> efferent arteriole -> peritubular caps

Vasa recta = peritubular caps of the juxtamedullary nephrons

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3
Q

What comprises the glomerular filtration barrier?

A
  1. Capillary endothelial cells
  2. Glomerular basement membrane
  3. Glomerular epithelial cells (podocytes)
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4
Q

What are barriers to glomerular filtration?

A
  • Size (MW under 5,500 = freely filtered)
  • Charge (major determinant for MW 5.5-44K, fixed negative charges on filtration surface)
  • Shape (minor determinant)
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5
Q

Names for inner tubule surface?

A

Luminal or apical

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6
Q

Names for outer tubule surface?

A

Peritubular or basolateral

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7
Q

What is reabsoprtion?

A

Transport of water/solutes form inside -> outside the tubule

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8
Q

What is secretion?

A

Transport of water/solutes form outside -> inside tubule

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9
Q

Urine volume = ?

A

Urine volume = filtration - reabsorption + secretion

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10
Q

What is the role of the proximal nephron (PCT or PST)?

A

Bulk reabsorption of water and solutes (Na, Cl, HCO3, glucose)

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11
Q

What is the role of the Loop of Henle (tDLH, tALH, TALH)?

A
  • Moderate solute reabsorption
  • Urine concentration and dilution
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12
Q

What is the role of the distal nephron (DCT, CND, collecting tubule- initial, cortical, outer/inner medullary)?

A
  • “Fine-tune” urine composition
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13
Q

What is the distribution breakdown of water in the extracellular vs. intracellular compartment?

A

Extracellular ~40% (17 L)

  • Blood plasma = 3 L
  • Interstitial fluid = 13 L
  • Transcellular fluid = 1 L

Intracellular ~ 60% (25 L)

(Total body water = 42 L)

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14
Q

Solute composition of plasma?

A
  • Na: 142
  • K: 4.4
  • Ca: 1.2 (ionized)
  • Mg: 0.6 (ionized)
  • Cl: 102
  • HCO3-: 22
  • Proteins: 7 g/dL
  • Glucose: 5.5 mM

pH = 7.4

Osmolality = 291

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15
Q

Volume balance: synonymous terms for intravascular volume?

A
  • Plasma volume
  • Effective circulating volume
  • 1/4 of extracellular fluid (ECF) volume

These determine blood pressure

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16
Q

In what conditions will you see a dissociation between total body volume and effective circulating volume?

A

Some disease states:

  • CHF
  • Cirrhosis
  • Kidney disease
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17
Q

T/F: Volume balance = water balance?

A

FALSE

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18
Q

Change in water balance changes what factors? Salt balance?

A

Change in water balance:

  • Relatively BIG change in osmolarity
  • Relatively SMALL change in ECF volume

Change in salt balance:

  • Reflected by ECF volume
  • Represents a minimal change in serum sodium (Na) osmolarity
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19
Q

Describe the renin-angiotensin-aldosterone axis (picture)

A
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20
Q

What triggers renin release? Inhibits?

A

Stimulated by:

  • Hypotension
  • Increased sympathetic outflow to JGA
  • Renal hypoperfusion (renal baroreceptors)
  • Endothelin, PGE2, PGI2

Inhibited by:

  • Hormones (Angiotensin II, AVP)
  • Other: high [K], nitric oxide
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21
Q

What triggers anigotensin II release?

A
  • Increase systemic blood pressure
  • Aldosterone release
  • Increase sensitivity of Tubuloglomerular feedback
  • Stimulate Na-H countertransport
  • Stimulate AVP and thirst centers
  • Efferent arteriolar vasoconstriction
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22
Q

ICF volume is a reflection of what?

A

Water balance/osmolarity

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23
Q

What are sensors of ICF volume?

A

Osmoreceptor input

24
Q

What are effector pathways of ICF volume

A
  • AVP (via ADH)
  • Thirst
25
What solutes are excreted by tubules: - Completely - Partially - Not at all
- Completely: **PAH** - Partially: **creatinine, Na** - Not at all: **glucose, bicarbonate**
26
Equation for arterial content?
(RPFa)(Px,a)
27
Equation for venous content?
(RPFv)(Px,v)
28
Equation for urine content?
(V)(Ux)
29
Equilibrium equation?
(RPFa)(Px,a) = (RPFv)(Px,v) + (V)(Ux) Basically, arterial content = venous content + urine content
30
Equation if solute is completely extracted?
Px,v = 0, therefore: (RPFa)(Px,a) = (V)(Ux) and (RPFa) = (Ux)(V)/(Px,a)
31
What is clearance?
Cx = (Ux)(V)/(Px)
32
What are characteristics of the ideal marker to estimate glomerular filtration rate? What is it?
- Freely filtered in the glomerulus - No tubular reabsorption or secretion - Not synthesized or metabolized - Physiologically inert This is Creatinine - Endogenous product of muscle metabolism - Easy to measure its value in the blood - Stable rate of production
33
Is creatinine filtered? Reabsorbed? Excreted?
- Filtered - NOT reabsorbed - Secreted
34
What is the rate of creatinine production for males/females?
Males: 15-20 mg/kg ideal body weight Females: 15-20 mg/kg ideal bod weight
35
Alternate markers to creatinine?
- Inulin (gold standard) - B12 - Iothalamate - EDTA
36
Clearance of creatinine estimates what?
The glomerular filtration rate (GFR)
37
What is normal GFR?
100-125 mL/min (adults) - Males \> females - Declines with age
38
Does stable serum creatinine = stable kidney disease?
No - The sCr is not a great marker also because it is maintained despite loss of GFR due to tubuloglomerulofeedback (recruitment of other gloms) and increased tubular Cr secretion 15% to 35%.
39
Results of regulation of GFR (glomerulotubular balance)?
Glomerulotubular balance: - No change in fractional excretion/reabsorption - High GFR -\> high absolute reabsorption / excretion - Low GFR -\> low absolute reabsorption / excretion - Prevents excessive changes in solute excretion
40
How is GFR regulate?
**1. Tubuloglomerular feedback (TGF)** - Macula densa (MD) senses changes in solute delivery (MD = specialized cells near distal tubule & vascular pole) - Results in release of vasoactive substances -\> change GFR **2. Neurohormonal effects- Vasoconstriction** - Angiotensin II: Arteriolar vasoconstricton efferent \> afferent - Arginine vasopressin: Renal vasoconstriction medulla \> cortex - Sympathetic nervous system activation - Modulators: epinephrine, endothelins, leukotrienes
41
Does anigotensin II vasoconstrict the afferent or efferent arterioles more?
Efferent \> afferent
42
What is the range of urine osmolality?
30-1200 mOsm (daily solute exretion ~ 600 mOsm)
43
What is the lowest possible urine volume? Highest?
**Lowest**: V = 600/1200 0.5 L/day **Highest:** V = 600/30 = 20 L/day
44
What is the osmolarity of the fluid entering the descending thin limb? In the medullary interstitium?
- Fluid entering tDL: 300 mOsm - Medullary interstitium: 1200 mOsm Established by the countercurrent multiplier system
45
What is arginine vasopressin?
Aka aldosterone or anti-diuretic hormone (ADH)
46
What is the mechanism of action of ADH? What stimulates/suppresses it?
- Insertion of water channels (aquaporins) into apical membrane in collecting ducts - Upregulate Na/K/Cl cotransport in thick limb - Insertion of urea transporters (UT1) into apical membrane in medullary collecting ducts - Stimulated by hyperosmolarity - Suppressed by hypoosmolarity
47
What are major hormones controlling phosphorus regulation?
**Parathyroid hormone (PTH)** - Decreases PO4 reabsorption (increases excretion) - Downregulates apical transporter expression 1,25-dihydroxy vitamin D - Increases PO4 reabsorption (decreases excretion) at distal nephron **Increase PO4 excretion:** - Increase intake - ANP - Glucocorticoids - Acidosis
48
Describe calcium regulation in terms of Na and other hormones?
- Increased Na reabsoprtion -\> increased Ca reabsorption (and vice versa); it follows Na! **- PTH**: increases Ca reabsorption in TAL, DCT, CCT - **Vitamin D:** increases Ca reabsorption in distal nephron **- Loop diuretics:** decrease Ca reabsorption
49
What is normal blood pH? Minimal urine pH?
- Normal blood: 7.4 - Minimal urine: 4.4
50
What is acidemia? What causes it?
Low pH of blood, caused by either: - Respiratory acidosis (high PCO2) - Metabolic acidosis (low HCO3) Acidemia does NOT = acidosis (acidemia is the net pH change; acidosis is the process leading to this)
51
What is alkalemia? What causes it?
High pH of blood caused by either: - Respiratory alkalosis (low PCO2) - Metabolic alkalosis (high HCO3) Alkalemia does NOT = alkalosis
52
What are the ECF buffers? Relative importance/effectiveness?
1. Bicarbonate (CO2/HCO3) 2. Proteins 3. Phosphate (H2PO4/HPO4)
53
What are the relevant equations for CO2/HCO3 buffer pair?
pKa of the bicarbonate buffer system = 6.1 pH = 6.1 + log (HCO3)/(CO2) pH = 6.1 + log (HCO3)/(PCO2 x 0.03)
54
Why is bicarbonate buffer system (pKa = 6.1) better than phosphate (pKa = 6.8)?
- [HCO3] \>\> [total phosphates] - Open system (respiratory adjustment of CO2 and renal adjustment of HCO3)
55
How does the kidney respond to respiratory processes? (speed, HCO3 handling...)
- Slow (hours or days) - Reclamation of filtered HCO3 - Increased titratable acid excretion - Very increased ammoniagenesis - H secretion = HCO3 reabsorption
56
How does the kidney respond to metabolic alkalosis?
**Suppression of proximal H+ secretion** - Inhibit basolateral Cl-HCO3 exchange - Increase HCO3 paracellular backleak **Suppression of ammoniagenesis** **Inhibit H+ secretion in Cortical Collecting Duct** - Decrease alpha-type intercalated cells (H+ secretion) - Increase beta type intercalated cells (HCO3 secretion)
57
Correction of metabolic alkalosis is very sensitive to \_\_\_\_\_\_\_\_. Elaborate
Correction of metabolic alkalosis is very sensitive to **ECF volume status** - Volume depletion limits ability to correct alkalosis 1. Decreased GFR = decreased filtered load HCO3 2. Decreased Na delivery = decreased Na reabsorption (Na-H exchange) 3. Decreased ECF volume = Increased aldosterone (Increased H+ secretion)

MS2 Renal (25 decks)

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